Experimental Investigation of Deep-Bed Filtration of Spark-Ignited, Direct-Injection Engine Exhaust Using Ceramic Particulate Filters

Viswanathan, S. Experimental Investigation of Deep-Bed Filtration of Spark-Ignited, Direct-Injection Engine Exhaust Using Ceramic Particulate Filters. University of Wisconsin-Madison, 2016.

Gasoline particulate filters (GPFs) provide an effective means of reducing particulate matter (PM) emissions from the SIDI exhaust. Filter pressure drop and filtration efficiency (FE) are the primary metrics used to govern GPF design. In the current study, a series of filter wall-scale experiments were performed to understand the impacts of filter and particle properties on filtration performance.

PM emissions from different steady-state SIDI operating conditions were characterized using different instruments. The relationship between particle mass and mobility diameter was independent of engine condition and the mass-mobility exponent was observed to lie within ~2.3 ? 0.15. An integrated particle size distribution (IPSD) method was used to estimate the mass concentrations in the SIDI exhaust. Average IPSD mass concentrations were 77?32 +47% of the gravimetric measurements performed using Teflon filters.

Mercury intrusion porosimetry (MIP) results showed that the filter samples used in this study had porosities ranging between 42?67% and median pore diameters (MPD) between 11?27 ?m. Permeability measurements indicated a smaller pressure drop across filters with narrower pore size distributions. Capillary flow porometry (CFP) measurements showed that the pore throat sizes fell within 1?30 ?m. Porosity distribution profiles obtained using X-Ray CT technique showed lower porosities at the filter surface compared to the rest of the wall.

The exhaust filtration analysis system (EFA) developed at the University of Wisconsin?Madison was used to perform wall-scale filtration experiments at a nominal temperature of 125 ?C for two different filtration velocities of 2.75 and 5.5 cm/s. Particle penetration showed weak dependence on inlet PSD or the range of particle shapes explored in this study. A 10% difference in surface porosity had little impact on the evolution of filtration performance. A significant impact of pore size distribution was observed on particle capture within the filter walls. Higher filtration velocity appeared to have a larger impact on penetration of 50-nm particles (P50) for filters with a narrower pore size distribution. A simplified cylindrical pore flow model was used to explain the trends observed from the filtration experiments. Preliminary filtration experiments at 600?C demonstrated the ability of the upgraded EFA system to perform in-situ filter regeneration studies.